resolveGlobalCacheDir

pub fn resolveGlobalCacheDir(arena: Allocator, environ_map: *const std.process.Environ.Map) ![]const u8 {
    if (EnvVar.ZIG_GLOBAL_CACHE_DIR.get(environ_map)) |value| return value;

    const app_name = "zig";

    switch (builtin.os.tag) {
        .wasi => @compileError("on WASI the global cache dir must be resolved with preopens"),
        .windows => {
            const local_app_data_dir = EnvVar.LOCALAPPDATA.get(environ_map) orelse
                return error.AppDataDirUnavailable;
            return Dir.path.join(arena, &.{ local_app_data_dir, app_name });
        },
        else => {
            if (EnvVar.XDG_CACHE_HOME.get(environ_map)) |cache_root| {
                if (cache_root.len > 0) {
                    return Dir.path.join(arena, &.{ cache_root, app_name });
                }
            }
            if (EnvVar.HOME.get(environ_map)) |home| {
                if (home.len > 0) {
                    return Dir.path.join(arena, &.{ home, ".cache", app_name });
                }
            }
            return error.AppDataDirUnavailable;
        },
    }
}